The present invention relates to methods for manufacturing a semiconductor photodetector whose spectral sensitivity is controlled to the visible light region.
As a photodetector, a CdS cell having spectral sensitivity characteristics as shown in FIG. 6 has been widely used. However, since cadmium is high in environmental burdens and falls under a controlled substance by RohS command of EU, cadmium will be prohibited to use within EU from July 2006. As a replacement of cadmium, a photodetector formed from silicon has been used. In order to compose a photodetector with a silicon phototransistor, spectral sensitivity characteristics of silicon (FIG. 7) needs to be coordinated with relative luminous characteristics (FIG. 8) which is sensitivity of human eyes.
In order to achieve this, conventionally, after fabricating a silicon light receiving element, an optical thin film filter composed of multiple thin films in which an oxide silicon (SiO2) film and a titanium oxide (TiO2) film are alternatively laminated has been provided at a light receiving surface of a silicon light receiving element within a vacuum plasma evaporating apparatus in an optical multiple thin film evaporation step 31 as shown in FIG. 9. The silicon light receiving element is adhered to a substrate in a die bonding step 32, and a wire is connected between the silicon light receiving element and a pad of the substrate in a wire bonding step 33. The silicon light receiving element is then sealed by a transparent resin in a transfer molding step 34 and is cut into individual semiconductor photodetectors in a separating step 35.
By the above-mentioned arrangement, spectral sensitivity of the infrared region within the spectral sensitivity of silicon is decreased by the optical thin film filter such that entire sensitivity can be approximated to relative luminous characteristics (FIG. 8) (see, for example Japanese Unexamined Patent Publication No. 15044/1997).
However, formation of an optical thin film filter of the multilayer thin film formed by alternatively laminating an oxide silicon (SiO2) film and a titanium oxide (TiO2) film is a troublesome task in terms of time and processes and results in high cost. In other words, the multilayer thin film is formed by multiple times of vacuum plasma evaporation, and a bonding pad is etched to be open for electrical connection after the formation of the multilayer film. These processes require special techniques in addition to the time consuming processes thus resulting in high cost.
An object of the present invention is to provide methods for manufacturing a semiconductor photodetector having spectral sensitivity characteristics close to relative luminous characteristics at low cost.